If X and Y are integers, is the value of X(Y+1) even?
(1)X and Y are prime numbers
(2) Y>7
Answer: C both statements together are sufficient, but neither statement alone is sufficient.
问一下为什么不是E？ 即使Y〉7，X，和Y都是质数，也可能X为2，这样就成了偶数，如果不是2 的数也就是奇数咯？这种想法对么。。。
Tanya prepared 4 different letters to send to 4 different addresses. For each letter, she prepared a envelpe with its correct address. If 4 letters are to be put into the 4 envelpe at random. What is the probability that only 1 letter will be put into the envelpe with its correct address? Answer: 1/3
请问怎么做的哦？ | 
